Lp. Christensen et al., EFFECT OF NITROGEN-FERTILIZER TIMING AND RATE ON INORGANIC NITROGEN STATUS, FRUIT COMPOSITION, AND YIELD OF GRAPEVINES, American journal of enology and viticulture, 45(4), 1994, pp. 377-387
A four-year (1987-90) trial was conducted to study the effects of timi
ng and rate of N fertilizer application on furrow-irrigated Barbera, G
renache, French Colombard, and Chenin blanc grapevines. The objectives
were to further determine optimum N fertilizer practices for importan
t wine cultivars in the San Joaquin Valley and to compare inorganic N
constituents, NO3-N and NH4+-N, for N status determination. The six tr
eatments included four N fertilizer application timings at budbreak (B
B), fruit set (FS), veraison (V), and post-harvest (PH) with a 56 kg N
/ha rate, as well as BB with a 2X rate of 112 kg N/ha and control (CO)
. Vine N status was determined by NO3--N and NH4+-N levels and their s
um, total inorganic N (TN), in bloom and veraison petioles. Yield and
fruit composition parameters were measured for vine response. Cultivar
responses varied widely, with Grenache and Barbera being the high and
low extreme cultivars, respectively, in petiole TN status and respons
iveness to N treatment; French Colombard and Chenin blanc were interme
diate. Generally, TN status increased with increasing N rate (CO BB56
BB112). Nitrogen fertilizer timing demonstrated that the more recent N
applications often resulted in a higher petiole TN status at the next
petiole sampling; i.e., PH56 and BB56 treatment petioles had higher T
N status at bloom while FS56 was higher at veraison. Post-harvest timi
ng was found to be particularly effective in supplying petiole TN in t
he spring; i.e., PH56 sometimes resulted in bloom petiole TN levels co
mparable to BB112 in all four cultivars and higher than BB56 in Grenac
he, French Colombard, and Chenin blanc. Petiole NO3--N levels were mor
e sensitive than NH4+-N levels to fertilizer treatment. The greater co
ntribution of NO3--N to TN and their high correlation coefficients as
compared to NH4+-N and TN would place in question the utilization of N
H4+-N as an additional measurement of N status. Grape soluble solids w
as the most responsive fruit parameter to N treatment. Generally, N fe
rtilizer decreased soluble solids over CO, irrespective of timing, and
with the highest rate (112 kg N/ha) resulting in the largest decrease
. Grape yields were only affected in Grenache, with all of the N treat
ments increasing yields over CO except V56. This result, plus other ne
gative effects of the V56 treatment, suggest that veraison was the lea
st desirable timing of those compared. Otherwise, timing effects on fr
uit parameters were minor.